Cathode-ray tube



Feb. '9, 1943. E, SCHANTL ET AL I 2,310,811

CATHODE-RAY TUBE Filed April 1, 1941 Patented Feb. 9, 1943 CATHODE-RAY TUBE Erich Schantl and Maximilian Messner, Berlin,

Germany; vested in the Alien Property Custodian Application April 1, 1941, Serial No. 386,267 In Germany March 29, 1940 3 Claims.

This invention relates to cathode ray tubes, also designated as Braun tubes, and it aims to provide devices of this kind which are easy to manufacture and to which a high accuracy of construction is peculiar, especially as regards the distance between the emitting cathode and the control electrode.

According to the invention, the cathode has a circumferential edge which is pressed against a spacing member located between the cathode and control electrode.

The invention will be understood from the following description and the accompanying drawing in which Fig. 1 is a fragmentary sectional view of one embodiment of the invention, and Fig. 2 is a sectional view of a modified form of cathode.

R denotes the bulb of a cathode ray tube. The emissive layer E of the cathode is carried by a plate P whose peripheral edge P is bent to form a generally frusto-conical portion extending preferably rearwardly with respect to layer E and a control electrode S arranged in front of this layer. The electrode S rests against an insulating body I1. The middle of the electrode S is shown to be in the shape of a funnel projecting toward the cathode P, E. This shape, however, is immaterial to the inventive idea. The electrode S has an aperture A in the middle. Through this aperture the electrons emerging from layer E are to pass. The plate P is pressed against the body I1 with the aid of an insulating body I2 provided with a recess B in which the plate P is located. Body I2 also contains a heating coil H which in the example here shown is a flat spiral arranged in a casing of insulating material. The leads h, h. for supplying heating energy to the coil H are located on the side remote from P, E. Owing to the described circumferential bend of the plate P this plate bears firmly against the body I1, such bend and the recess B being so calculated that the plate P is compressed to some extent when assembling the device. The pressure of P against I1 increases when the cathode becomes hot; but the distance between P, E and S is not varied thereby since P, E is prevented by I1 from moving toward S. Only the peripheral bend of P may yield laterally, the diameter of recess B being somewhat larger than that of the plate P. In this way the distance between emissive layer and control electrode will be independent of the operating temperature of the cathode ray tube. The described construction also allows of making the distances between the several component parts small, this being desirable in many cases in order to shorten the length of such tubes.

The plane shape of the cathode P, E is merely shown by way of example. The form thereof is susceptible of variation, provided that there is a circumferential generally frusto-conical edge arranged to be compressed by the bodies I1, I2. For instance, the cathode may be formed as shown in Fig. 2, with a funnel-shaped projection. that extends toward the electrode S and is coated at its apex with the emissive layer. In such case the control electrode may be plane in its turn. Also, modifications of such conical cathode may be employed. The conical cathode has the advantage that 'a field concentration occurs at its apex and that consequently the main emission takes place at the apex with the result that the emissive layer need not be arranged very carefully.

Means of any suitable kind may be employed for holding the parts I1, I2, S together. For instance, spring clips C may serve this purpose. Where I1 and I2 are of the same diameter, this being the case here illustrated, a tube D of metal, glass or insulating material may be inserted over them to center these parts and at the same time to aid in holding them together.

What is claimed is:

1. A cathode ray tube including a cathode and a control electrode, an insulating body between said cathode and control electrode for establishing the spacing therebetween, another insulating body on the side of said cathode remote from said control electrode, at least one of said bodies having a cavity therein for retaining said cathode therein, said cathode having a yieldable preformed peripheral edge for urging said bodies to separate from each other when pressed together, centering means inserted over said bodies and said control electrode for aiding in holding them together, and spring clip means for holding said bodies from separating and for holding said control electrode in" position relatively to said body and said cathode.

2. A cathode ray tube according to claim 1, in which said cathode consists of a plate having a peripheral edge bent rearwardly from the emission surface of said cathode for providing said yieldable preformed edge.

3. A cathode ray tube according to claim 1 in which a heating element is provided in a casing of insulating material in said cathode retaining cavity.

ERICH SCHANTL. MAXIMILIAN MESSNER. 

